Method and apparatus for guiding multiple-thickness rug pile and the like with photoelectric cell means contacting the pile



Juiy 11, 167 P. v. COLOMBO 3,330,962

METHOD AND APPARATUS FOR GUIDTNG MULTIPLE-THICKNESS RUG FILE AND THE LIKE WITH PHOTOELECTRIC CELL MEANS CONTACTING THE FILE Filed July 27, 1964 3 Sheets-Sheet 1 E. mm hm mm mm 5 1 3? INVENTOR.

PAUL V. COLOM BO ATTORNEYS July 11, 1967 P. v. COLOMBO 3,339,962

METHOD AND APPARATUS FOR GUIDING MULTIPLE-THICKNESS RUG FILE AND THE LIKE WITH PHOTOELECTRIC CELL MEANS CONTACTING THE FILE Filed July 27, 1964 3 Sheets-Sheet 2 i 8 5K n Q Lif- 9 o "l (I) w w v Q INVENTOK M PAUL V. COLOMBO BY 0) 2 wavy/ M 0 u. DE 4:! I

ATTORNEYS Juiy 11, 1957 P. v. COLOMBO 3,330,952

METHOD AND APPARATUS FOR GUIDING MULTIPLE-THICKNESS RUG FILE AND THE LIKE WITH PHOTOELECTRIC CELL MEANS CONTACTING THE FILE Filed July 27, 1964 3 Sheets-Sheet 3 FIG. 4

FIGS

2 l i 1: l l l I l I344 I 3 o I H 1434 I: 1 132 132 I W:

I 6 L715" 1 yy' WV "I I29 INVENTOR PAUL V. COLOMBO M,WZ

ATTORNEYS United States Patent Paul V. Colombo, Mount Vernon, N.Y., assignor to Mount Hope Machinery Company, Lindsay, Ontario, Canada, a Canadian company Filed duly 27, 1964, Ser. No. 385,437 14 Claims. (Cl. 250-419) This invention relates to an improved method and apparatus for guiding sheets or webs having multiple thicknesses, such as rug pile; and more particularly to an improved method and means for detecting and controlling the lateral position of an offset running edge of a multiplethickness sheet or web, which is offset from the outer lateral edge of the sheet or web.

Rug piles, and other multiple-thickness webs such as laminated sheets having offset edges, have commonly been guided according to the position of the outermost edge or selvage, as it is quite difficult to guide the offset edge of the piling itself. Conventional methods such as pneumatic or mechanical sensing have not resolved the problem of pile guiding, inasmuch as the relatively thin outwardly-protruding selvage interferes with the sensors conventionally used. Efforts have been made to utilize photoelectric methods, by gauging the differential in reflectivity as between the selvage and the pile. This approach encounters great difficulty from the varying reflectivity of multicolored and variously-patterned rug piles, and the usually-slight difference in reflectivity between the selvage material and the pile.

It is the primary object of the present invention to pro vide an improved method and apparatus for detecting the lateral position of an offset relatively thick portion of a multiple-thickness sheet, and for guiding the offset edge along a predetermined path of travel.

It is another object to utilize one or more photoelectric cells in an improved manner for the detection and guidance of a multiple-thickness web such as a rug pile. It is a further object to guide a pile material having a sculp tured surface or a scalloped edge in an improved manner. Further objects and advantages of the invention will appear as the following description proceeds.

Briefly stated, according to a preferred practice, I may carry out the method of my invention by directing a light source against the surface of a multiple-thickness sheet or web at a fixed point along a desired path of travel of the thicker edge, which is offset from an outer lateral edge of the sheet; I then position at least one photoelectric cell along or adjacent the path in such a position that it will be physically obscured by direct engagement with the thicker portion whenever this portion overlaps the desired path. Consequently, the cell will be shaded when the thicker portion overlaps the fixed path, but will become illuminated and will undergo a change of state as a result of the relative change in light intensity in the event the thicker portion drifts in the opposite direction. The state of the cell can then be determined for the purpose of indicating the offset edge position, or may be applied by various circuits for controlling sheet-guiding means to correct any tendency of the sheet to wander away from the desired path.

According to a preferred practice, I utilize two photoelectric cells, placing them in opposite lateral directions from the desired path to establish tolerance limits for a permissible degree of straying of the offset edge from its path. Provided the offset edge remains within the tolerated zone of deviation, one of the cells remains obscured while the other is illuminated. A state either of illumination or of obscuration of both cells indicates a departure of the offset edge from its predetermined path, and the direction of that deviation.

In a preferred form of apparatus incorporating dual photoelectric cells, the cells are incorporated in individual bridge circutis which energize individual relays; the relays are connected in a manner to actuate web-guiding means in one correctional sense upon obscuration of both ceils and in an opposite correctional sense upon illumination of both cells. Consequently, the energization of either relay alone produces no guiding action, and the oifset edge is permitted to wander within the tolerance limits established by the lateral spacing between the two cells. Alternatively, one or more cells may be incorporated in a single bridge circuit or in conventional circuits for detection or guider-control purposes, with somewhat different operational characteristics.

According to a further feature of the invention, the photoelectric cells are mounted in an singularly-adjustable head carried by one of a pair of confronting jaws, between which the selvage and pile edge of the web are slidably received. The light source is also mounted in the sensing head, along its axis of adjusting rotation; variation of the tolerance limits is therefore obtainable simply by altering the angular position of the sensing head with respect to the direction of Web travel.

For the satisfactory operation of this apparatus, it is necessary as a practical matter that the cells or their casing substantially contact the thicker portion of the sheet, to 'be obscured by its passage beneath them. To provide for the accommodation of varying sheet thicknesses, I prefer to mount the sensing head in a movable jaw which is spring-biased toward a pre-selected position corresponding to the nominal sheet thickness.

The invention is also useful for guiding rug pilings having sculptured surfaces or scalloped edges. A modified form of cell placement is preferred for these purposes; each of a pair of cells is positioned substantially along the desired path of the pile edge, and a cell spacing is used which differs somewhat from the spacings of the ridges or scallops in the pile edge. Alignment of the two cells along the pile path would ordinarily produce a continuous hunting action, since both Cells would at any given time be either illuminated or obscured; however, the passage of ridges and hollows tends to offset the hunting action, since first one cell and then the other becomes temporarily illuminated. Since the responses of conventional guiding mechanisms involve some time delay, the aligned arrangement actually tends to reduce hunting action when applied to a sculptured or scalloped pile.

While the specification concludes with claims particularly pointing out the subject matter which I regard as my invention, it is believed that a clearer understanding may be gained from the following detailed description of preferred embodiments thereof, referring to the accompanying drawings, in which:

FIG. 1 is a view in elevation and partially in section of a detection apparatus embodying the invention, and shown in operative relation to one edge of a rug pile;

FIG. 2 is a plan view of the device of FIG. 1;

FIG. 3 is a schematic diagram showing a preferred control circuit for use with the detection apparatus, together with web-guiding means;

FIG. 4 is a schematic diagram showing another form of control circuit;

FIG. 5 is a plan view showing a modified form of sensing device for use with a rug pile having a scalloped edge, as illustrated; and

FIG. 6 is a view in elevation showing the apparatus of FIG. 5 applied to a rug pile having a sculptured surface.

Referring to FIGS. 1 and 2, a preferred form of the improved detection apparatus includes a mounting head 10, which is supported in vertically-adjustable relationship upon a machine frame member 12 by means of a threaded standard 14 and adjusting nuts 16. Horizontal adjustment of the mounting head is provided by means of ways 18 slidably supporting the head in a guide block 20; the adjustment is brought about by a hand wheel 22 which carries a worm (not shown) cooperating with a horizontal rack (not shown) formed on the ways 18, or otherwise acts through suitable mechanism to adjust the head position.

The mounting head carries guiding jaws 24 and 26, which slidably receive one edge of a multiple-thickness web such as a rug pile 28, traveling longitudinally in the direction indicated by the arrow. The illustrated rug pile includes a relatively thin backing terminating in a selvage 30, and a relatively thick pile which terminates in a laterally-offset edge 32. The apparatus serves to guide the pile edge along a predetermined path, without reference to the location of the selvage 30'. The protruding portion of the backing remains attached to the pile temporarily for manufacturing convenience, and is later removed; for purposes of processing the pile it is, therefore, desired to guide the pile edge rather than the selvage.

According to the invention, a pair of photoelectric cells 34 and 35 are mounted in diametrically-spaced relation within suitable bores 36 and 37 formed in a cylindrical sensing head 38, and are arranged for conditional illumination by a bulb 40, which is received within a bore 42 centered on the axis of the sensing head. An opening 44 through the upper arm 24 receives the sensing head, which is adjustably mounted and secured therein by means of set screws 46 cooperating with a circumferential recess 48. By these means, the angular relation of the cells 34 and 35 with respect to the indicated direction of web travel may be altered, as suggested in dotted lines in FIG. 2, so that the tolerance limits may be adjusted by changing the lateral spacings of the cells with respect to the pile edge. Electrical connections for the cells and the lamp are made by a cable 59 with a control circuit to be described, by way of an automatic or manual selector switch 52, so that the automatic control can be overridden and controlled by manual push-button switches 54 if desired.

The spacing of the jaws 24 and 26 is adjustable to conform to the pile thickness of the material being handled, so that the active face 56 of the head 38 may be coincident with the plane of the exposed pile surfaces. However, it is desirable to avoid any substantial drag against the pile, as this would tend to distort the pile material as it passes through the arms. The movable jaw 24 is mounted slidably by means of a stud 58 threaded therein, and by jaws 60 which are received upon parallel guiding walls 62 formed in the housing The stud 58 is slidably received through a pair of eyes 64 protruding from the housing, and has a collar 66 adjustably aifixed thereto for cooperation with compression springs 68 and 70. The position of the collar determines a neutral position of the movable arm, toward which it is biased by the opposed compression springs. A further collar 72 is afiixed to the upper end of the stud to limit its dovmward motion with respect to the housing.

In the horizontal position shown, the backing of the web may tend to lie fiat against the fixed arm 26, but as it may be desired to position the head vertically in some applications, a guide shoe 74 is aflixed under the arm 24 to ensure that the backing does not accidentally obscure the cell 35 and give a false indication.

It will be apparent from an inspection of FIGS. 1 and 2 that so long as the pile edge follows a path lying intermediate the cells 34 and 35, one of them will be illuminated by the lamp 40, through reflection from the backing of the web, while the other will remain obscured by direct engagement with the pile. Wandering movement of the web to the right will, upon exceeding the tolerance limit, result in the obscuration of both cells, while a movement in the opposite direction will result in illumination of both. The states of the cells are determined and compared, and the position of the pile edge with respect to the predetermined path is indicated by this comparison.

A preferred form of circuit means is shown in FIG. 3, for comparing the conditions of the cells automatically, and ultilizing this information to control a web guider for correcting any lateral displacement of the web in excess of tolerance limits. Each of the photocells 34 and 35 is incorporated in one leg of an individual bridge circuit, which has a pair of balanced resistors 80 and an adjustable potentiometer 82 forming the remaining legs. Power is supplied to each bridge by a transformer 84 and a full-wave rectifier 86, having a choke coil 88 and a capacitor 9% connected in parallel for smooth ing the supplied DC. current. The photocells 34 and 35 are of a type which effectively block current flow when obscured, but present relatively little resistance when illuminated.

While the bridge circuits may be utilized for the direct energization of guider-control relays, the preferred circuit shown employs amplifying transistors 94 and 96,

which in this case are of the NPN type, to amplify the relatively weak photocell currents for energizing control.

relays 98 and 100, respectively. The relays are powered by rectifiers 102 and 104, respectively, connected to the corresponding transistors. Base signal current is supplied by connecting the negative lead of each rectifier through a corresponding bridge circuit and thence to the transistor base. Each base is provided with a diode 106 to block the application of negative potential. A zener diode 108 is connected in parallel with each relay coil to cause surge currents generated by the collapse of the coil field to be bypassed from the transistor.

In the condition shown it is assumed that each photocell is obscured, so that the relays are de-energized. If either cell is illuminated, the resulting photocell conduction causes a positive bias to appear at the base of the corresponding transistor, and thus the corresponding relay is energized. At the same time, the bridge circuits are preferably so balanced that a negative bias is applied to the blocking diodes at the bases of the transistors at such times as the photocells are obscured, thus effectively preloading the transistors against firing during a momentary or incomplete illumination of the controlling photocells, and preventing undue sensitivity of response.

Each relay includes a pair of contacts 110' and 112, the contacts 110 of each relay being connected in series -to control the energization of a first solenoid-actuated valve 114, and the contacts 112 .of each relay similarly being connected in series to energize a second solenoid-actuated valve 116.'The control valves 114 and 116 are arranged to control the supply of compressed air from a suitable t source to either of two single-acting control motors 118 or 120, which are connected to tilt the ends of a guide roll 122 in either angular sense. According to conventional practice, the web is passed over the guide roll, and may be guided laterally in either direction by appropriately tilting the roll. The motors 118 and 120 are provided with suitable spring return means (not shown), so that. the roll is caused to assume a neutral position, perpendicular to the direction of web travel, when both motors remain de-energized.

In the illustrated de-energized condition of both relays, occurring during obscuration of both photocells, the contacts 112 are closed to energize the valve 116 and actuate the motor 120 to tilt the roll 122 in the direction shown,

thereby to return the web in a direction to uncover the and the roll is thus returned to a neutral position as the.

pile edge re-enters a neutral zone between cells. The cell remaining uncovered and illuminated continues to energize its relay, so that the circut of each control valve remains broken.

Should the pile edge wander in the opposite direction far enough to illuminate both cells, each of the relays will become energized, with a consequent reversal of both sets of contacts to complete a circuit through the contacts 110 to actuate the valve 114 and the motor 118. The resulting reversal of the angular tilt of the guide roll will return the pile edge in the opposite lateral direction until it returns once more to the neutral zone between cells.

It may be desired to provide a proportional control, that is, a control of the angle of tilt of the guide roll which is proportionately related to the relative degree of illumination of the two cells, while the pile edge remains within the tolerance limits. Thus, correction may be initiated before a wandering edge has completely transversed across either cell. In this type of control, the amplified signals produced by the transistors may be applied directly to the voice coils of a servo-valve (not shown) which regulates the position of the guide roll. The relays 98 and 100 with their contacts 110' and 112, and the solenoidactuated valves 114 and 116, would thus be replaced in the illustrated circuit by the servo-valve.

According to a further embodiment of the control circuit, a single bridge as shown in FIG. 4 incorporates both photocells 34 and 35, connected in parallel in one leg of the bridge. The transistors 94 and 96 are connected across the bridge in reversed relationship, being incorporated in individual relay circuits as in the preceding embodiment. The circuit is balanced in such a way that if either cell is illuminated and the other shaded, an intermediate value of effective resistance is maintained which results in a neutral condition, and neither transistor is energized. However, should both photocells become illuminated, or both become shaded, the alteration of effective resistance of the photocells causes one or the other of the transistors, as the case may be, to become energized. To incorporate this single bridge modification in the circuit of FIG. 3, however, it is necessary to reverse the contact arrangement of one of the relays 98 or 100, so that energization of either relay combined with de-energization of the other, will produce a control action of a corresponding sense; whereas de-energization of both relays will break both solenoid-valve circuits. The single-bridge circuit, is however, not preferred, because the moderate change of resistance as between a neutral condition and the illumination of both photocells, i.e., dividing the effective photocell resistance in half, requires rather delicate balancing of the circuit. The inclusion of adjustable resistance means may be desirable to assist in obtaining a proper balance.

In a modified form of the circuit of FIG. 4, which is not illustrated, one of the photocells is omitted; the circuit is otherwise identical, and the basic mode of operation remains the same, although the balance of the bridge is much more delicate. An intermediate degree of illumination, through a relatively narrow range of intensities, maintains both transistors in a non-conductive state; while a variation in light intensity activates one transistor or the other, depending upon the sense of the variation and the consequent polarity of current flow.

It is often necessary to handle rug pilings having sculptured surfaces or scalloped edges, and a modification of the photocell arrangement which is especially useful in such applications is shown in FIGS. 5 and 6. A pile having a scalloped edge is illustrated at 126 in FIG. 5, having an offset selvage 128. The sensing head 130 is provided with a pair of photocells 132 which are spaced along the desired average path of the scalloped pile edge, at a spacing substantially different from the peaks of the edge pattern. Since the spacing may be quite substantial, each cell is provided with an individual lamp 134 located closely adjacent thereto. In consequence of the unphased spacing of the cells with respect to the scallop pattern, one cell is obscured while the other is illuminated, and the relationship is reversed sequentially. The illustrated control circuits are unaffected by alteration of the relationship, so long as either cell is energized and the other obscured, with the result that the control will remain in active so long as the pile edge substantially follows the average path. In the event that the pile edge deviates substantially in either direction, both cells will become illuminated or obscured, depending upon the direction of the deviation, and control action will be initiated as in the preceding embodiment. It should be understood that two pairs of cells incorporated each in a circuit as in FIG. 3, may be used in place of the individual cells shown in FIG. 5.

A similar result is obtained by applying the sensing head to a rug pile having a straight pile edge but a scalloped surface, as illustrated in FIG. 6. In an analogous manner, the cells 132 are spaced out of phase with the peaks of the sculptured pattern, and a similar mode of control action ensues. However, I have found that a systern having a single photocell also gives satisfactory results in this application.

In some cases, the protruding selvage portion or thinner layer of the multiple-thickness sheet being guided may be of irregular width or even non-existent; it should be understood that a photocell exposed by the pile or thicker layer will then be illuminated by reflection from the surface of the jaw 26 in the embodiment of FIGS. 1 and 2. In other applications, any back-up surface may be arranged to reflect light to the exposed cell or cells in the event that the thinner layer is irregular, altogether missing, or even transparent, as would be the case where an opaque thicker offset layer is laminated with a transparent or translucent thinner backing layer.

It should be understood that while the illustrated circuitry has been described with reference to photoelectric cells of the photoconductive type, in which variation in incident light produces a resistance change, the invention may be applied to cells of the photo-voltaic type, in which current is generated in relation to the incident light.

While I have described preferred embodiments of my invention by way of illustration, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the invention, which I therefore intend to define in the appended claims without limitations to the details of the foregoing embodiments. It will also be apparent that the improved method and apparatus may be applied to the guiding of laminated materials, folded paper and board, and many other multiple-thickness materials which have an offset edge whose lateral position is to be detected and controlled.

What I claim is:

1. The method of detecting lateral displacement relative to a preselected path, of an elongated longitudinallytraveling multiple-thickness sheet having a relatively thick central portion with a major surface terminating in a longitudinal edge offset inwardly from a relatively thin selvage portion thereof, by means of photoelectric cell means and a light source, which comprises the steps of: directing the light source against said major surface of the sheet at a fixed point along a preselected path of travel of said oifset edge; positioning the photoelectric cell means along the preselected path in position to substantially contact said major surface when the latter laterally overlaps the preselected path so that the photoelectric cell means is then physically occulted by engagement with said central portion, but is illuminated when said central portion does not overlap the preselected path; and detecting the state of the photoelectric cell means to determine the existence and sense of any lateral displacement of said offset edge relative to the preselected path.

2. The method of detecting lateral displacement relative to a preselected path in excess of selected tolerance limits, of an elongated longitudinally-traveling multiplethickness sheet having a relatively thick central portion with a major surface terminating in a longitudinal edge offset inwardly from a relatively thin selvage portion thereof, by means of a pair of photoelectric cells and a light source, which comprises the steps of: directing the light source against said major surface of the web at a fixed point along a preselected path of travel of said offset edge; positioning the photoelectric cells with opposite lateral spacings from the preselected path corresponding to selected tolerance limits and each in position to substantially contact said major surface when the latter laterally overlaps the position of that cell, so that the cell is then physically occulted by engagement with said central portion, but is illuminated when said central portion does not laterally overlap the position of that cell; and detecting and comparing the resulting states of each cell to determine the existence and sense of any lateral displacement of said offset edge in excess of said tolerance limits, relative to the positions of said cells.

3. The method of guiding, along a predetermined path, an elongated longitudinally-traveling multiple-thickness sheet, having a relatively thick central portion with a major surface terminating in a longitudinal edge offset inwardly from a relatively thin selvage portion means of a photoelectric cell means and a light source, which comprises the steps of: directing the light source against said major surface at a fixed point along a predetermined path of travel of said offset edge; positioning the photoelectric cell means along the predetermined path in position to substantially contact said major surface when the latter laterally overlaps the predetermined path so that the cell means are then physically occulted by engagement with said central portion, but are illuminated when said central portion does not laterally overlap the predetermined path; detecting the resulting state of the cell means; and guiding the sheet in one lateral direction upon detecting occultation of the cell means, and in the opposite lateral direction upon detecting illumination of the cell means, the direction of guiding being chosen to guide said edge toward said predetermined path.

4. The method of guiding, along a predetermined path within selected tolerance limits, an elongated longitudinally-traveling multiple-thickness sheet having a relatively thick central portion with a major surface terminating in a longitudinal edge offset inwardly from a relatively thin selvage portion thereof, by means of a pair of photoelectric cells and a light source, which comprises the steps of: directing the light source against said major surface at a fixed point along a predetermined path of travel of said offset edge; positioning the photoelectric cells with opposite lateral spacings from the predetermined path corresponding to selected tolerance limits and each in position to substantially contact said major surface when the latter laterally overlaps the position of that cell, so that that cell is then physically occulted by engagement with said central portion, but is illuminated when said central portion does not laterally overlap the position of that cell; detecting the resulting state of each cell; guiding the sheet in one lateral direction upon detecting occultation of both cells, and in the opposite lateral direction upon detecting illumination of both cells, the direction of guiding being chosen to guide said edge toward said predetermined'path; and discontinuing said guiding upon detecting disagreement between the states of the two cells.

5. Apparatus for guiding, along a predetermined path, an elongated longitudinally-traveling multiple-thickness sheet having a relatively thick central portion with a plane major surface terminating in a longitudinal edge ofiset inwardly from a relatively thin selvage portion thereof, said apparatus comprising, in combination: at least one photoelectric cell; a light source for said photoelectric cell; sensing heads means supporting said cell and said light source at fixed points spaced apart along said pre-' said offset edge; said sensdetermined path of travel of said ing head being constructed and arranged to support thereof, by r cell in closely confronting relation to the plane of said major surface such that said central portion engages said sensing head and physically occults said cell from illumination by said light source when said edge travels along said predetermined path, and light is directed from said source against said selvage portion for reflection therefrom to illuminate said cell upon displacement of said central portion in one direction from said predetermined path; together with circuit means for detecting the state of said cell to determine the existence and sense of any lateral displacement of said offset edge from the predetermined path; sheet guiding means for effecting lateral displacement of said sheet; and guiding control means operatively connected with said sheet guiding means and said circuit means; said guiding control means being constructed and arranged to produce guiding action in one lateral direction upon detection of occultation of said cell, and in the opposite lateral direction upon detection of illumination of said cell, the such as to guide said edge toward the predetermined path.

6. Apparatus as recited in claim 5, in which said sensing head means comprises a pair of jaws having opposed plane surfaces, receiving said sheet slidably therebetween, support means supporting one of said jaws stationarily and the other slidably relative thereto for accepting varying sheet thickness, and means biasing said jaws together to engage said central sheet portion closely therebetween.

said predetermined path of travel of said offset edge, said,

second cell and light source being spaced from the firstmentioned cell and light source a distance differing substantially from said periodic dimension.

8. Apparatus for guiding, along a predetermined path, an elongated longitudinally-traveling multiple-thickness sheet having a relatively thick central portion with a plane major surface terminating in a longitudinal edge offset inwardly from a relatively thin selvage portion thereof, said apparatus comprising, in combination: a pair of photoelectric cells; a light source for said photoelectric cells; a sensing head supporting said light source at a fixed point along said predetermined path of travel of said offset edge; said sensing head being constructed and arranged to support said cells in closely confronting rela tion to the plane of said major surface and with opposite lateral spacings from the predetermined path corresponding to selected tolerance limits, whereby said central portion engages said sensing head and physically occults said cells from illumination by said light source when said central portion overlaps the lateral positions of said cells and light is directed from said source against said selvage portion for reflection therefrom to illuminate either of being constructed and arranged to produce guiding action,

in one lateral direction upon detection of occultation of both of said cells by said circuit means, to produce guiding action in the opposite lateral direction upon detection of illumination of both of said cells by said circuit means, the direction of guiding being such as to guide said edge toward the predetermined path; said guiding control means discontinuing guiding action upon detection by said circuit means of disagreement between said cells.

9. Apparatus as recited in claim 8, in which said sensg head means comprises a pair of jaws having opposed direction of guiding being for detecting and comparing plane surfaces receiving said sheet in snugly slidable relation, and a sensing head received through one of said jaws and having a plane terminal surface coinciding with the plane surface of said one jaw, said cells and said light source being mounted in said sensing head and said sensing head having openings in said terminal surface for individually exposing each of said cells and said light source to said sheet.

10. Apparatus as recited in claim 9, in which said sensing head is angularly adjustable about an axis normal to said plane terminal surface thereof, said openings being arranged to expose said light source at the intersection of said axis with said terminal surface, and to expose said cells at different points spaced apart from said axis, whereby said tolerance limits may be adjusted by angular displacement of said sensing head.

11. Apparatus as recited in claim 8, in which said circuit means comprise a pair of relays each having an energizing coil and at least one set of contacts, a pair of transistors each having a controlling circuit connected to a different one of said cells and a load circuit including a different one of said relay coils and a source of current, each controlling circuit biasing the corresponding transistor to conduct current in its load circuit when and only when the cell in its control circuit is illuminated, and controlled circuit means actuated by said contacts to energize said guiding control means to produce guiding action in one or the other lateral direction according as said cells are both illuminated or both occulted, said controlled circuit means being de-actuated by said contacts as said cells are dilferently illuminated.

12, Apparatus as recited in claim 11, in which each of said controlling circuits comprises a bridge incorporating one of said cells and being balanced when that cell is occulted, and imbalanced by illumination of that cell to bias the corresponding transistor to conduct current in its load circuit.

13. Apparatus as recited in claim 8, in which said circuit means comprise a pair of relays each having an energizing coil and at least one set of contacts, a controlling circuit incorporating said cells in parallel relation, a pair of transistors connected in reversed bias relation to said controlling circuit and each connected to a dilferent load circuit including a difierent one of said relay coils and a source of current, said controlling circuit biasing one transistor to conduct current in its load circuit when and only when both cells are illuminated and biasing the other transistor to conduct current in its load circuit when and only when both cells are occulted, and controlled circuit means actuated by said contacts to energize said guiding control means to produce guiding action in one or the other lateral direction according as said cells'are both illuminated or both occulted, said controlled circuit means being de-actauted by said contacts as said cells are differently illuminated.

14. Apparatus as recited in claim 13, in which said controlling circuit comprises a bridge incorporating said cells in parallel relationship in one leg thereof, said bridge being balanced while either of said cells is illuminated and the other occulted, and being imbalanced with opposite polarity according as both cells are illuminated or occulted in common.

References Cited UNITED STATES PATENTS 2,411,513 11/1946 Bergier ct a1 250202 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,330,962 July 11, 1967 Paul V. Colombo It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the printed specification, lines 6 to 8, for "assignor to Mount Hope Machinery Company, Lindsay, Ontario, Canada, a Canadian company" read assignor to Mount Hope Machinery Company, Taunton, Mass., a corporation of Massachusetts Signed and sealed this 19th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents 

1. THE METHOD OF DETECTING LATERAL DISPLACEMENT RELATIVE TO PRESELECTED PATH, OF AN ELONGATED LONGITUDINALLYTRAVELING MULTIPLE-THICKNESS SHEET HAVING A RELATIVELY THICK CENTRAL PORTION WITH A MAJOR SURFACE TERMINATING IN A LONGITUDINAL EDGE OFFSET INWARDLY FROM A RELATIVELY THIN SELVAGE PORTION THEREOF, BY MEANS OF PHOTOELECTRIC CELL MEANS AND A LIGHT SOURCE, WHICH COMPRISES THE STEPS OF: DIRECTING THE LIGHT SOURCE AGAINST SAID MAJOR SURFACE OF THE SHEET AT A FIXED POINT ALONG A PRESELECTED PATH OF TRAVEL OF SAID OFFSET EDGE; POSITIONING THE PHOTOELECTRIC CELL MEANS ALONG THE PRESELECTED PATH IN POSITION TO SUBSTANTIALLY CONTACT SAID MAJOR SURFACE WHEN THE LATTER LATERALLY OVERLAPS THE PRESELECTED PATH SO THAT THE PHOTOELECTRIC CELL MEANS IS THEN PHYSICALLY OCCULTED BY ENGAGEMENT WITH SAID CENTRAL PORTION, BUT IS ILLUMINATED WHEN SAID CENTRAL PORTION DOES NOT OVERLAP THE PRESELECTED PATH; AND DETECTING THE STATE OF THE PHOTOELECTRIC CELL MEANS TO DETERMINE THE EXISTENCE AND SENSE OF ANY LATERAL DISPLACEMENT OF SAID OFFSET EDGE RELATIVE TO THE PRESELECTED PATH. 